Hepatic steatosis — US / CT / MRI

USCTMRICross-modality steatosis criteria

Detection and grading of diffuse hepatic steatosis across modalities.

Applies to

Assessment of suspected fatty liver on ultrasound, unenhanced CT, or MRI

Does not apply to

Contrast-enhanced CT attenuation (unreliable for fat quantification)
Focal fat that mimics a lesion — describe as pseudolesion, not steatosis

What to report

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1.US echogenicity
Grade against renal cortex: mild (increased echogenicity), moderate (obscured vessels), severe (obscured diaphragm/deep liver).
2.CT attenuation
Unenhanced liver attenuation and liver−spleen difference. Liver <40 HU or liver−spleen ≤ −10 HU indicates moderate–severe steatosis.
3.MRI quantification
Chemical-shift signal drop or PDFF for fat fraction; PDFF is the most accurate.
4.Distribution
Diffuse versus focal; note geographic sparing near the gallbladder fossa and porta hepatis.
Pitfall: Focal fat and focal sparing follow no mass effect and respect vessels — do not call them lesions.
5.Coexisting findings
Iron overload (which confounds MRI fat estimates), fibrosis features, and portal-vein visualization on US.

Scores & calculators

CT hepatic steatosis

Liver fat estimate from unenhanced CT attenuation.

Liver attenuation

Spleen attenuation

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Applies to UNENHANCED CT only. Liver − spleen ≤ −10 HU, or absolute liver attenuation < 40 HU, indicates moderate–severe steatosis. Contrast-enhanced attenuation is unreliable.

MRI fat fraction (two-point Dixon)

Estimated hepatic fat fraction from in-phase and opposed-phase signal.

In-phase signal

Opposed-phase signal

Complete the inputs to see the result.

Two-point Dixon estimate: FF = (IP − OP) / (2 × IP) × 100. Confounded by iron and valid only up to ~50% fat. Dedicated PDFF sequences are preferred; thresholds are approximate.

Sources

CT quantification of liver fat — Kodama Y et al. AJR (2007)
MRI-PDFF of hepatic steatosis — Reeder SB et al. J Magn Reson Imaging (2011)

Content review: Content pending clinical review · 2026-07-09

Educational reference for trained clinicians. Verify every result against the cited original guideline before use. Not a substitute for clinical judgment or medical advice.